The invention relates to a means for locking a drive shaft of a fuel injection pump of an engine in a definite position, especially a position that corresponds to the initial point of injection, by means of a device the position of which is fixed relative to the pump housing. By means of this device a force and friction fitted connection, which holds the drive shaft in a set definite rotary position, can be produced by means of an element that is firmly attached to the drive shaft.
With fuel injection pumps of series construction it is necessary to restrain the position of the cam shaft and its first cam at the point when fuel injection is to take place, that is the rotary position which corresponds to the beginning of injection should be properly confined in order to be able to install the injection pump with the internal combustion engine. In distribution type fuel injection pumps the drive shaft is normally held in a set rotary position which is correlated with the initial point of injection.
Heretofore, in order to be able to designate this supply beginning position, it has been required to correlate several indicia points, e.g., one would apply an index line on a part connected firmly to the drive shaft with a second index line applied to the front side of the pump, or with an index line on a movable part, if the fixed index has been applied to the pump housing. This known type of adjustment has the serious disadvantage that the index line may not be visible from the outside if the pump is mounted with its front flange secured to the gear casing of the internal combustion engine. When a pump is being mounted on the internal combustion engine it is often necessary to have to start all over to determine the initial point of injection. This can be done by the so-called "overflow method," and is achieved when the disassembled pressure valve of the pump suction chamber is placed under fuel pressure and the pump with a coupled and stationary drive shaft is slowly rotated until the pump piston, by its upward stroke, closes the suction bore and fuel stops flowing. In this position the fuel injection pump, now set at the initial injection point, is secured into place with the internal combustion engine. This method of adjustment takes a great deal of time and can only be performed by highly-trained technicians. Thus it is apparent that even with accessible index lines the adjustments which must be made during installation of the pump on the internal combustion engine is very dependent on the skill of the mechanic.
Locking assemblies for a drive shaft of a fuel injection pump that is capable of restraining the drive shaft at an initial injection point are known (DT-AS No. 24 38 313). These devices include a locking pin which is pressed against a surface of the part connected with the drive shaft, with this surface being arranged coaxially of the drive shaft axis and uniformly cylindrical in the area of installation of the locking pin. A spring is acted upon radially from the outside toward the drive shaft axis, and thus produces a force and friction fitted connection to thereby lock the drive shaft in the desired rotary position. Although the force acting on the drive shaft is limited by the spring, there is nevertheless a force loading the drive shaft which is not desirable. In addition, it is disadvantageous that a uniformly cylindrical surface must always be available and arranged coaxially to the drive shaft axis so that the manner of positioning the device with respect to the pump or governor is fixed in advance. Pump or governor housings must, in addition, be provided for the mounting of the device. The assemblying of the device with an internal combustion engine is also dependent on the specific location under the bonnet or hood where it may be placed and a uniform installation is not possible even for the same pump or governor models unless it is for use with identical engines.